Is president trump on the verge of victory? He thinks so, and tonight, he's making that promise that if passed, Americans will see savings within weeks. Tonight, Republican leaders in both the house and the senate have now agreed on a single plan. President trump making what the white house called his closing argument today. This even egg, what does this mean for the middle class versus wealthier Americans? And what does it do to the deficit? And will it pass? ABC's Mary Bruce, leading us off. Reporter: At the white house today, Republicans proclaimed they're on the verge of a big win on tax reform. The president with a Christmas promise. We want to give you, the American people, a giant tax cut for Christmas. And when I say giant, I mean giant. Reporter: But back on the hill, protests. Kill this bill! Kill this bill! Reporter: Protesters say it will hurt the working and the middle class, as lawmakers huddled in the basement of the capitol to finalize the bill. Even top Republican negotiators admit it's not a totally done deal. So do you have a deal? Ah -- well, it's going forward. Very positive. It feels very close. Reporter: Even the president is cautious. I mean, we are so close right now, so close, in fact, almost -- I don't want to talk about it. Maybe we shouldn't talk about it. Reporter: Tonight, they have agreed to this. Helping corporations, it drops the corporate tax rate from 35% to 21%. Caps the mortgage interest deduction at $750,000, a middle ground between the senate and house versions. Repeals the Obamacare individual mandate that all Americans have insurance, which could leave 13 million more Americans without insurance in the next decade. And to help the wealthy, it lowers the top individual tax rate from 39% down to 37%. How does that help middle class Americans? This bill is going to lower the tax burden on working families, on middle income families and it's going to generate tremendous economic growth. Reporter: But what about the deficit? It's still unclear how much this will ultimately cost. A new analysis predicts it could add more that $1.5 trillion to the nation's debt. And a previous analysis of the senate version said Americans making $75,000 or less will pay more over the next ten years. Democrats insist the long-term benefits will go to the wealthy. Most of what's there for the middle class is written in disappearing inning. The Republican tax bill is one that ebenezer scrooge would love. It is a big bah humbug. Reporter: Democrats are urging Republicans to slow down and wait until the new democratic senator from Alabama, Doug Jones, is sworn in. But the pressure is on for Republicans to pass this before the GOP loses that Alabama vote. If it doesn't get done before then? Well, it could be a problem. There could be a problem at that point. Mary Bruce with us live on the hill tonight. We heard the president today promise that if he has the bill by Christmas, Mary, that Americans will see lower taxes and bigger paychecks by February. Is that true? Reporter: David, we've been pressing the white house for answers, and calling the irs. No response yet from the irs, but the white house insists that starting in February, Americans benefits from the tax cut will see less money withheld from their paychecks. And real quick, Mary, democratic leaders pushing for congress to wait for a tax vote until Doug Jones, the Democrat who won in Alabama last night, is sworn in in the senate. But that's not likely to happen. Reporter: David, there is very little chance of that happening. Doug Jones' victory last night puts even more pressure on Republicans to pass tax reform here and fast. David? Mary Bruce leading us off. In the meantime, to that

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